Fume-proof electric switch device



Ufl tifd FUME-PROOF ELECTRIC SWITQH DEVICE Otto Heuberger, Biuningen, and Paul Mayer, Basel, Switzerland, assignors to Ciba Limited, Basel, Switzerland Application May 21, 1956, Serial No. 586,143

Claims priority, application Switzerland May 23, P955 1 Claim. (Cl. filth-51.69)

As the operation of electric switches is accompanied or may be accompanied by sparking, which is liable to cause the ignition of explosive gas mixtures, it is known that all electric switch devices must fulfil especially high requirements when they are installed in places where explosive gas mixtures may be formed. This is especially the case when switch devices are installed in store rooms, in which inflammable and relatively easily volatile liquids are stored, because there may be present for periods of hours or days explosive gas mixtures which diffuse into electric switch devices and are therefore liable to be exploded by sparking in the electric switch devices.

On the other hand, there is the possibility that explosive gas mixtures may be formed for short periods of time from vapours occurring transiently in rooms in which work is normally carried out, for example, in factories and laboratories connected with the chemical industry, surgical operation, theatres, etc. However, rooms of this kind, owing to the purpose for which they are used, are ventilated and during working hours, which is the only time when explosive vapours can be formed, are hardly ever left unattended for long periods, so that explosive gas mixtures cannot remain undisturbed for long periods in such rooms, whereas fumes of explosive or inflammable gases may well pass by electric switches. It is desirable also in these cases so to protect electric switch devices that in the event of the accidental presence of explosive vapours these devices cannot cause ignition or explosion. However, it is not necessary that the protection should be so thorough as to be effective against the continuous presence of explosive gases for periods of days. It is sufficient so to construct the electric switch devices that, for a period of a few hours, explosive gas mixtures cannot penetrate by difiusion from the exterior into the interior of the closed device although the closure may not be absolutely tight.

The present invention provides a fume-proof electric switch device, which comprises a quick break switch having contact elements which are closed and opened upon the movement of a rockable lever past a dead centre position, an enclosure within which the said switch is housed so as to be substantially inaccessible to gases, and a control member which is movable to transmit motion from outside the enclosure to the rockable lever therein for closing and opening the contact elements, the said movable control member being located so as to prevent substantial diffusion of gases to the interior of the enclosure.

Advantageously a switch device in accordance with the invention is combined with the socket portion of a plug and socket connector, and the said control member is movably mounted so as to transmit motion to the rockable lever by way of a substantially difiusion-resisting guide or bore. The arrangement may be such that the plug portion does not move the control member until the plug portion is almost completely inserted. By

2,827,523 Patented vMar. 18, 1958 2 thus combining the quick break switch with a plug and socket connector it is ensured that sparking cannot occur upon inserting and removing the plug portion, because the socket portion is not live, and the making orbreaking of the switch contacts takes place only when the socket portion has made proper contact with the plug portion and therefore no sparking can occur at those parts which are not protected against vapours.

In this construction the control member actuating the quick break switch advantageously takes the form of a pin movable parallel to the axis of the socket portion, and advantageously provided in the axis of a socket and guided in a manner substantially resistant to gas difiusion, such as a closely fitting bore of suflicient length.

Apparatus constructed in accordance with the invention is shown by way of example in the accompanying drawings in which Fig. l is a plan view of the socket portion of a plug and socket connector having a safety earth connection and with the protective cover removed,

Fig. 2 is a section taken on the line II in Fig. 1 with the quick break switch closed,

Fig. 3 is a section. taken on the line II in Fig. 1 with the quick break switch open,

Fig. 4 shows a plan view of the quick break switch only, and

Fig. 5 shows a modification in the form of a tumbler switch having a manually operable lever.

In all the figures 11 denotes a cylindrical supporting base made of a suitable insulating material, for example, an artificial resin or more especially a ceramic material and having a strong upwardly directed supporting surface. By means of a cover plate 12 which, when the apparatus is completely assembled, is fixed in a suitable manner, for example, by glue or cement, a practically air-tight closed space is formed, which contains the quick break switch. 011 the supporting surface of the base are fixed, for example, by screws terminals 13 for the two poles of the current and a terminal 14 for the earth lead. There are also mounted on the base resilient sockets 15 to receive the pins of the plug portion and also a socket 16 for the earthing pin of the plug portion. Within the socket 15 there is proveded a control member in the form of a pin 17 which is axially slidable in the base with little'play. -In- Figure 2 the pin is shown in its lowermost position and in Figure 3 in its uppermost position. The lower part of the pin 17 is housed within a space which is closed air-tight by means of an extensible bellows 13. As shown in Fig. 2 the bellows 18 are in the extended position and in Fig. 3 in the collapsed position.

The pin 17 and bellows 18 are in contact with a rocking lever 19. The latter is rockable about a spindle 20 which is fixed in a frame 21. The frame is fixed to and in metallic contact with the terminals 13. By means of a spring 22 the rocking lever is pressed into the upper position shown in Fig. 3, provided that the pin 17 through the bellows 18 does not depress the lever 19 into its lowermost position under the influence of an external force, namely upon the insertion of the plug pin 45. The rocking lever 19 has a lower part 23 which terminates in a notch 24, in which a contact lever 25 is held by a spring 26. This contact lever carries at its other end a contact head 27 which together with a contact head 28 makes and breaks contact with the socket 15. The contact bead 28 is fixed to and in metallic contact with the socket 15 through a metal member 29 and screw 30.

The operation of the switch device is as follows:

When the plug portion is fully inserted the pins 45 of the plug are in their lowermost position (see Fig. 2) and they depress the pin 17, which in this construction is broken all the other is' advantageously made of insulating material, and the rocking lever 19, 23 is in its lowermost position and the Contact 27, 28 is closed. When the plug is pulled out of the sockets, the rocking lever is lifted, under the action of the spring 22 and the contact lever 25 is first moved slightly to the left,'whereby any slight sintering of the co ntact bead 27 to the contact head 28 which may occur due to the action of strong currents, is broken. Then, after the dead centre position has been passed, the contact lever is suddenly withdrawn into the lowermost position shown in Fig. 3 and the circuit is broken. This breakin'g'of the circuit takes place within the closed space formed'by'the hollow base 11 and the plate 12, and occurs before the plug pin 45 has lost metallic contact with the socket 15, so that no external sparking can occur. At this instant, however, the socket 15 is not live, so that when the plug pin 45 is finally withdrawn from the socket 15 no sparking can occur.

Advantageously'the device of this invention is protected against any unintended separation of the terminal 13 from the wire 43 (for example, through some vibration or percussion). This is accomplished by providing theterminal 13 with a cap, screw 31 inside of which are a spring 32 and a pin 33 which'hold 'wire 43 in position. As a result, when the cap screw 31 is slightly loosened the wire 43 is still held in place by the spring 32 and the pin 33, so that no sparking can occur.

Figure illustrates the same principle as applied to an ordinary manually operated tumbler switch. The pin 17 is in this case operated by the switch lever 35 which is mounted .eccentrically on a pivot 34. The positions of the parts when the pin 17 is in its uppermost position, are shown in fulllines, and in broken lines when the pin is in its lowermost position in which the circuit is broken. The quick break switch itself is constructed in the same manner asin Figs. 2' and 3, so that it is only incompletely shown in.Fig..5. n

t The switch device shown in Figs. 1-5 may be modified in certain respects. Thus, for example, in most cases the bellows 18, may be dispensed with by arranging that the pin 17 shall move in its guide or bore with very little play.- Furthermore, instead of connecting the contact head 28 to the socket which receives a plug,-it may be connected to the'terminal 13, and in this .case it is not necessary to construct the pin 17 of insulating material, because immediately after the contact 27, 28. parts of the switch device are free from current. a 1 p I inally, instead of the notch 24, there may be provided a pivot.

The quick break switch and its enclosure shown in Figs. 1 to 3, owing to its compact construction, may be built into the socket portion of a wall plug and socket happen due to exceptionally unfavorable circumstances.

It is a great advantage of the construction shown in Figs. 13 that it requires very little space while affording all the protection against fire and explosion hazards normally required and that therefore no changes are necessary with most of the usual supports for the conventional unprotected wall plug and socket connectors. It is furthermore surprising that even without the use of completely gas-tight closures the protection is excellent. 7 t

What is claimed is: 7

A plug and socket connector having connecting' means accessible from theoutside for inserting a connecting plug, a base portion carrying said connecting means and being of customary size and dimensions but forming a hollow bottom portion, a quick breaking switch in the circuit between the main line and one of the connecting means, and located in said hollow space, and a cover forming together with said hollow base portion an enclosure within which said switch is housed so as to be substantially unaccessible to gases, and a control member, movable to transmit motion from outside the enclosure'to said switch for opening or closing it, said movable member being located so as to prevent substantial diffusion of gases to the interior of the enclosure, said control member being actuated by insertion of the connecting plug in such a manner that the plug makes electrical connection with the socket before the switch is actuated, the entire connector having a size not exceeding that of a conventionalplug and socket connector so that'it may be mounted in a housing in place of such a conventional connector.

References Cited in the file of this patent UNITED STATES PATENTS 1,612,711 Erikson Dec. 28, 1926 1,731,893 Fischer Oct. 15, 1929 FOREIGN PATENTS 634,753 Great Britain Mar. 29, 1950 862,190 Germany Ian. 8, 1953 

